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                [Baltic 2011]Plagiarism                </h1>
                <p>时间限制：1s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div align="center"></div>
<div style="text-indent: 24pt"><span style="font-size: 12pt">世界编程大赛的选手们提交</span><span style="font-size: 12pt">N</span><span style="font-size: 12pt">份程序文件</span><i><span style="font-size: 12pt">f</span></i><sub><span style="font-size: 12pt">1</span></sub><span style="font-size: 12pt">, &hellip;, <i>f</i><sub>N</sub></span><span style="font-size: 12pt">给评测系统。在将评测结果正式公布之前，评委会想要排除一切可能的剽窃现象。他们已有一个对比程序，用来比较两份程序文件，并判断它们是否太过相似了。</span></div>
<div style="text-indent: 24pt"><span style="font-size: 12pt">然而程序文件的数目相当大，把每两份（一对，</span><span style="font-size: 12pt">pair</span><span style="font-size: 12pt">）文件都进行比较的话将花太多的时间。另一方面，许多对</span><span style="font-size: 12pt">(pair)</span><span style="font-size: 12pt">可以直接被排除，如果文件的大小相差太大的话。</span></div>
<div style="text-indent: 24pt"><span style="font-size: 12pt">更准确地说，评委会决定，如果每两份文件（一对，</span><span style="font-size: 12pt">pair</span><span style="font-size: 12pt">）中，较小文件的体积小于较大文件的体积的</span><span style="font-size: 12pt">90%</span><span style="font-size: 12pt">，那将直接不比较这样的一对</span><span style="font-size: 12pt">(pair)</span><span style="font-size: 12pt">。所以，对比程序只比较这样的一对</span><span style="font-size: 12pt">(<i>f</i><sub>i</sub>, <i>f</i><sub>j</sub>)</span><span style="font-size: 12pt">：</span><span style="font-size: 12pt"> i&ne;j, size(<i>f</i><sub>i </sub>)&le; size(<i>f</i><sub>j </sub>)</span><span style="font-size: 12pt">且</span><span style="font-size: 12pt">size(<i>f</i><sub>i </sub>)&ge;0.9∙size(<i>f</i><sub>j </sub>)</span><span style="font-size: 12pt">。</span></div>
<div style="text-indent: 24pt"><span style="font-size: 12pt">编写程序计算有多少对</span><span style="font-size: 12pt">(pair)</span><span style="font-size: 12pt">文件需要被比较。</span></div>
<div></div></p><hr/><h3>输入格式</h3><p><div>&nbsp;</div>
<div style="text-indent: 24pt"><span style="font-size: 12pt">第</span><span style="font-size: 12pt">1</span><span style="font-size: 12pt">行包含一个整数</span><span style="font-size: 12pt">N</span><span style="font-size: 12pt">，即提交的程序文件总数。</span></div>
<div style="text-indent: 24pt"><span style="font-size: 12pt">第</span><span style="font-size: 12pt">2</span><span style="font-size: 12pt">行包含</span><span style="font-size: 12pt">N</span><span style="font-size: 12pt">个整数</span><span style="font-size: 12pt">size(<i>f</i><sub>1</sub>), &hellip;, size(<i>f</i><sub>N</sub>)</span><span style="font-size: 12pt">，每个整数代表文件的体积大小。</span></div>
<div style="text-indent: 24pt"></div></p><hr/><h3>输出格式</h3><p><div style="text-indent: 24pt"><span style="font-size: 12pt">第</span><span style="font-size: 12pt">1</span><span style="font-size: 12pt">行，也是唯一的一行，给出一个整数，即需要被比较的文件的对</span><span style="font-size: 12pt">(pair)</span><span style="font-size: 12pt">的数目。</span></div>
<div><b><span style="font-size: 14pt">数据范围</span></b></div>
<div style="text-indent: 24pt"><span style="font-size: 12pt">1&le; N &le;100 000</span></div>
<div style="text-indent: 24pt"><span style="font-size: 12pt">1&le; size(<i>f</i><sub>i</sub> ) &le;100 000 000</span></div>
<p><span style="font-size: 12pt">有</span><span style="font-size: 12pt">50</span><span style="font-size: 12pt">分的测试点中，</span><span style="font-size: 12pt">1&le; N &le;2 000</span></p></p><hr/><h3>样例输入</h3><pre>5
1 1 1 1 1</pre><hr/><h3>样例输出</h3><pre>10</pre><hr/><h3>提示</h3><p><div style="text-indent: 24pt"><span style="font-size: 12pt">第</span><span style="font-size: 12pt">2</span><span style="font-size: 12pt">个样例中，每两个文件之间都要互相比较（当然，每对只比较一次，不是两次）。</span></div></p><hr/><h3>题目来源</h3><p>没有写明来源</p>
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